Marketers will be shifting budgets away from traditional and toward interactive media—search, online display ads, email, social media, and mobile marketing—bringing about a decline in overall advertising budgets during the forecast period, Forrester said.

That trend is also a reflection of marketers' growing recognition of where consumers are spending their time, according to the report: "Marketers are getting better at balancing channel investments with consumer media time."

Though people typically spend equal amounts of their media time—34-35% in 2009—with television and the internet (including at work), TV ad spending is about four times that of internet ad spending (31% vs. 7%).